I don't think swapping the springs will work. I usually weld a extension on the front of the perch with the locating hole in that.
The original rear end mounting is about 1 1/2" back from the spring center bolt. Because the tires and wheels look like they are set too far forward in the wheel opening originally I set the rear end back a little farther, about 2". The e'brake cables limit you from moving it back any more.
